1. Field of the Invention
The invention relates to a rolling bearing unit including a rolling bearing and a grease supply portion that supplies grease to the rolling bearing.
2. Description of Related Art
A rolling bearing unit including a rolling bearing and a grease supply portion that supplies grease to the rolling bearing is described in, for example, Japanese Patent Application Publication No. 2011-58520 (JP 2011-58520 A). In the rolling bearing unit, an annular grease reservoir forming member in which a grease reservoir is formed is arranged radially inward of a spacer located adjacent to an outer ring of the rolling bearing. The grease reservoir forming member has a clearance forming piece having a distal end face on which projections that contact, at their distal ends, a step face of the outer ring are formed. Gaps between the step face and portions of the distal end face of the clearance forming piece, at which no projections are formed, serve as passages through which base oil of grease is introduced from the grease reservoir to a raceway surface of the outer ring.
However, if a certain kind of grease is used in the bearing unit described in JP 2011-58520 A, base oil is less likely to be separated from the grease. In this case, there is a possibility that the base oil will not be supplied to the raceway surface, causing adverse effects on lubrication of the bearing. Separation of the base oil from the grease is promoted by heating the grease. However, the grease reservoir forming member is located apart from the bearing. Therefore, the heat generated through the operation of the bearing is less likely to be transmitted to the grease reservoir forming member, and separation of the base oil from the grease is less likely to be promoted. For some rotary shafts that rotate at high speed, such as a spindle of a machine tool, a cooling system may be provided. The cooling system is provided in a housing and used to cool a bearing fitted to the rotary shaft. Thus, an increase in the temperature of the bearing due to the operation of the rotary shaft is suppressed. However, when the influence of the cooling system is exerted from the housing on the bearing fitted to the rotary shaft, separation of the base oil from the grease is further less likely to occur, causing a possibility that satisfactory bearing lubricating performance will not be ensured.